Real-time location (RTL) systems have become popular in recent years. Conventional RTL systems typically use radio frequency (RF) transmission to determine location. The RF based methods typically do not provide enough accuracy to support room and sub-room level accuracies. A few systems utilize infrared (IR) transmission as a localization method. The conventional “IR method” typically employs an IR transmitter on a portable device (i.e. a tag) and IR receivers in base stations that are scattered in rooms and corridors within the enclosure. A portable device ID is typically received by one of IR the base stations and the location of the portable device is determined based on its vicinity to a base station. A tag based IR transmitter typically needs a line of sight between the transmitter and a receiver (i.e. a base station) in order to robustly detect the device ID. This type of RTL system, thus, is occasionally prone to a lack of reception by the receiver base stations when the line of sight is blocked, making it susceptible to reliability problems. Also, these types of IR base stations are presently wired both for power and connectivity because they use IR receivers that are “open” at all times. The need for wiring increases the installation complexity and cost.
There is also another type of IR system that employs IR transmitters at the base stations and IR receivers at the portable device which attempts to solve the problem of poor IR sensitivity, by transmitting substantially higher power levels than wired stationary base stations are typically capable of. This system may address the sensitivity problem but does not address the wired installation problem. Furthermore, in order to make sure that the IR signal is readily available to the portable device at all times, the IR base stations transmit the IR signals at a very high burst repetition rate. The first installations of such systems generally failed because of an unexpected problem; the IR base stations interfered with TV remote controls that are a part of is almost all patient rooms in hospitals. To solve the problem, newer systems transmit the IR signals much less often, with a severe penalty on tag power consumption (because the tag needs to search for the IR signal with an open IR receiver).